36$ FISHES. 



Upon the whole, the absorption of the oxygen is very feeble, and 

 it has been computed that a man consumes fifteen thousand times 

 more air than a tench. 



exceeded the latter in a still greater proportion. The fresh was about the standard 

 of common air, and the foul somewhat worse than the air in which a candle just goes 

 out : it might have been worse, but the water remained in an open vessel all night 

 before the experiment. Hence, air contained in water in an unelastic state is as 

 necessary to the life of fishes, as air in an elastic state is to that of land animals. 



He then had no doubt but that putting fishes into water impregnated with air 

 thoroughly phlogisticated would be equally injurious to them, as this air in an elastic 

 state is to land animals ; and this was verified. He began with rain water which 

 contained no air, having been recently boiled. He put nine small fishes into a 

 vessel containing about three pints of it, and they lived between three and four 

 hours, no air having been admitted. Two fishes were put into a pint of it impreg- 

 nated with phlogiston from air that had been phlogisticated six months before by 

 means of iron filings and sulphur, and they lived in it nearly an hour. It was very 

 imperfectly impregnated. Inflammable air had a similar efi'ect. John Hunter 

 having informed him that fishes would not live in water impregnated with fixed air, 

 be tried it, and found that small fishes would not live in it more than a few minutes. 

 It is well known that all spa waters containing fixed air are fatal to fishes, frogs, 

 and insects. He found that in water impregnated with nitrous air they were 

 affected in the same manner, but more violently ; but as a decomposition of some 

 small part of the nitrous air might take place before he could possibly slip the 

 funnel into the neck of the phial, he introduced the fishes into the vessel in which he 

 had impregnated the water while it remained inverted in the basin, the remainder of 

 the nitrous air not imbibed by the water still resting upon it. The phial contained 

 something more than a pint, and the nitrous air occupied about one-fourth of it. 

 Into this vessel he introduced two small fishes, and they continued very quiet, with- 

 out being seized with any conv-ulsions (as happened before), ten minutes, or a quarter 

 of an hour, before they died. Hence, the cause of the convulsions, in the former 

 experiment, arose not from the nitrous air, properly speaking, but nitrous acid, which 

 acted like the fixed air, another kind of acid. Whereas now the fishes were no 

 otherwise affected than in water with phlogisticated or inflammable air, except that 

 the water had imbibed more of the nitrous air, and hence was sooner fatal to them. 



Broussonet, a French chemist, was the next who made experiments on fishes. 



On the 20th of June, 1784, Broussonet put a couple of ten-spined stickle-backs 

 (epinoches) into some water at a temperature of 14 degs. This was gradually heated, 

 and at the end of two hours and a half the thermometer mounted to 28 degs. : the 

 fishes then became agitated, but on being cast into fresh water they became well 

 again in a few minutes. 



On the 10th of November, 1784, he put a carp, some bleaks, gudgeons, and perch, 

 into some water of the Seine at 5 degs., and the bottom of the vessel was covered 

 with sand. At 25 minutes past twelve o'clock the thermometer was at 6^ degs. ; at 

 30 minutes at Sdegs., &c. This experiment lasted tUl 45 minutes past four; and 

 he marked the degrees of heat every five minutes, pouring some fresh water into the 

 vessel at dififereut times in small quantities. At 12 degs., the smallest fishes began 

 to rise to the surface of the water, became agitated and ill ; yet the Seine water is 

 much warmer in the summer. At 21 degs. the small bleaks were nearly dead. At 

 22 degs. the perch were motionless and reversed. The gudgeons, which were of a 

 larger size, did not appear to suffer till 23 degs. ; whilst the carp was not at all 

 agitated, its respiration being only more frequent. At 28 degs., at which point the 

 water was kept 15 minutes, the carp began to lose its equilibrium, and became ill ; it 

 afterwards appeared dead, and only came to itself again after being left a long time 

 in fresh water. Broussonet employed four hours and a half in bringing the heat of 

 the water to 28 degs. He is of opinion that, with certain precautions, fish would 

 live in a water heated beyond 28 degs. 



But the experiments on which the greatest reliance is deservedly placed, are these 

 of Sir Humphrey Davy, who resolved on ascertaining the truth of the power which 

 had been long attributed to fishes, namely, that they could decompose water into 

 oxygen gas. The following is an account of his experiments. 



